This invention relates to defining and projecting sound phrases with qualities for optimizing mission effectivity and reducing undesirable side effects of emergency vehicle (EV) audible warning systems.
Since their advent, motorized vehicles have been adapted and used to transport personnel and equipment for missions categorized as civilian emergencies. These missions include e.g., transporting law-enforcement personnel to the scene of a crime, the transport of firefighters and their equipment to the scene of a fire, the transport of medical personnel and equipment to the scene of an accident, and the transport of accident victims or critically ill patients to a hospital. Since time is of the essence in all of these missions, sirens and systems have been developed for EVs to warn individuals to yield all rights-of-way and to allow free passage. As the size, power and speed of EVs have increased, the possibility of serious damage and bodily injury from a collision with pedestrians or other vehicles (including other EVs) has become a major consideration in the design of warning systems. Certain warning systems are emitters of audible signals which have the advantages of propagating around blind corners and being perceivable from all cranial azimuth angles by human observers. The primary requirement of producing a sound that is loud enough to be heard at a sufficient distance drove the early designs of EV audible warning systems. As EV speed capability increased, so did the necessity for projecting the audible warning signal to increasingly greater distances. This gave rise to hand and motor driven mechanical sirens, and to electrosolenoid and pneumatic driven resonant horns. The limitations of these technologies dominated the properties of the warning sounds, generally characterized by either the continuous wail of the rotary siren, or the alternating high and low pitch tones of a dual horn (European) system.
Modern EV audible warning systems have replaced mechanical sirens, electrically driven klaxon resonators, and pneumatic acoustical energy sources with high power electrodynamic linear transducers (loudspeakers) driven by efficient solid-state electronic amplifiers. However, the traditional warning sounds have become so entrenched that, in spite of the broad capabilities of linear driver/transducer systems, only the historically precedent warning sounds are emulated by present electronic siren systems (with the exception of the rapidly frequency-modulated sound commonly called the "yelp"). No existing commercially produced electronic siren system provides a sound, or class of sounds, specifically designed to optimize the success of the EV mission i.e. get to its destination in the shortest possible time, minimize the risk of collision with pedestrians and other vehicles, and at the same time reduce the negative side effects of audible warning systems as much as possible.
Emergency vehicles presently employ an audible warning system consisting of a sound generator which emits a continuous audible warning signal having a fixed sequence of frequency modulation. In all but electronic siren systems, this program is limited to a single repeating pattern. Electronic siren systems typically provide the means to manually select from among a small number of frequency modulation patterns. However, in no presently existing systems are there means for either manually or automatically controlling other attributes of the warning sound, e.g., tone quality (spectral content), amplitude and frequency pattern time profile, and pattern repetition rate.
The following is an enumeration of significant deficiencies of present siren sounds which compromise the effectivity of an EV's primary mission, and diminish the quality of the urban acoustic environment:
1. Because present warning signals are continuously sounded, the driver of an EV, necessarily subjected to the high intensity of his vehicle's warning sound, cannot hear the approach of other EVs. Since most emergency scenarios involve multiple EVs, often approaching the same point from different directions, this deficiency is manifested in the large number of accidents involving a collision between two EVs.
2. The present warning signals are grossly deficient in the psychoacoustic features which provide directionality (locatability) cues. Presently existing EV audible warning systems provide the observer with very little information about the EV, only that it exists somewhere in a local region and, depending upon the acoustical environment, perhaps some vague idea of the relative direction of the source. With such little information, he cannot assess the degree of impending danger, and therefore cannot react in an appropriate manner to avoid interference with the progress of the EV and to minimize his risk to personal injury and/or property damage.
3. By being forced to assume a worst-case level of danger, the observer is subjected to a substantially higher level of psychological and physical stress than is most often required to take appropriate accident avoidance measures, if, in fact, any at all are required. These higher stress levels may also impair the observer's judgmental abilities so as to frighten and/or confuse him into taking counterproductive responses that would actually increase the risk of accident. The present warning signals result in unnecessary psychological and physiological stresses to the general population (especially those in dense urban environments), the vast majority of whom have no need to alter their behavior to enhance the effectivity of the EV mission.
4. Some of the present warning signals produce highly negative conditioned emotional responses because of their association with the horrors of past wars and events, i.e. air-raid sirens and patrol vehicle high-low horns used during the holocaust.
5. Because present warning signals are continuously sounded, they soon lose the attention of the hearer, being perceptually relegated to the background noise level.
6. Present warning signals subject accident victims or critically ill patients to unnecessarily high stress levels when transported by ambulance.
7. Present warning signals are not optimized in their spectral, temporal, or directional characteristics for the purpose of penetrating to the interiors of other road vehicles in the projected path of the EV. The high road-noise isolation body designs and powerful auto audio entertainment systems of modern private vehicles make this consideration increasing more important.
8. The current noise abatement criteria for judging the annoyance of sounds solely by their loudness is both inadequate and misleading, i.e., it is possible to make soft sounds which are very annoying and loud ones which are quite pleasing. Two extreme examples might be the soft scraping of a fingernail on a blackboard and the sound of a large waterfall at a distance of ten feet. It is clear that the annoyance or pleasantness of a sound is a complex human reaction which relates to many factors including the nature or characteristic of the sound itself and the set of associations we have with it. As it is imperative that EV warning sounds be sufficiently loud in order to reach their intended hearers, a goal of this invention is the design of a set of sound patterns which are both more humane and more effective by the manipulation of other sound parameters.
The primary attribute of the sounds which is exploited and controlled in this concept is a psychological quality herein referred to as urgency. It is the degree of this attribute present in the sound which affects the observer's level of physiological response. High levels of urgency elicit high levels of awareness and autonomically trigger the body's defensive mechanisms (increased pulmonary and coronary rates, etc.); and low levels of urgency cue the observer that little or no response is required, thus sparing him unnecessary stress. The three characteristics of the sound which strongly correlate with subjectively perceived urgency are repetition rate, direction of frequency modulation (that is to say whether the frequency of tones in a phrase is ascending or decending), and relative content of high-frequency components. These characteristics are readily interpretable by the general population as strongly correlative with the sense of urgency without requiring any formal learning process. They are naturally associated with everyday dynamic events involving hazardous levels of speed and energy (e.g., the rate of the sound of railroad wheels crossing a rail joint increases as the train velocity increases, the whine of an engine increases in frequency as it accelerates, the high-frequency hiss steam makes escaping under high pressure, etc.). The essential features of this class of sounds, however, have not been utilized in audible warning systems for EVs. A goal of the invention is an attempt to mediate the urgency of the sound according to the hearer's particular degree of danger.